Francois,
Here is a gif of Nb2O5 at Nb K-edge and TiO2 at Ti K-edge. Both collected withb same geometry and detectors and same BL (SSRL 11-2). Fluo was collected at 90° to the beam (while transmission data was collected on the exact same sample).
both spectra are normalized. Is there not any remaining self-absorption in the fluo spectrum for Nb2O5, despite data collected at 90° ?? (while TiO2 sounds fine, as Troeger predicted ?).
Clearly - like you say -, for Nb2O5, the amplitude of the fluorescence scan is reduced compared to the transmission data. Nevertheless I'm more surprised that the TiO2 scans match even near the absorption edge. Although I find it hard to discuss your experiments without knowing the details here are two ideas that came to my mind: * You can't get an exit angle of exactly 90 deg, it's always a bit smaller. Therefore selfabsorption won't vanish completely * The amplitude damping, even at identical geometries, depends on which fraction of the overall absorption coefficient comes from the absorber. (The damping is something like mu_absorber(E)/(mu_tot(E)+g*mu_tot(E_fl)) .) I would expect this fraction to be larger and the selfabsorption to be worse for Ni.
and anyway one needs a code with all the angles allowed to vary.
As far as I understand the mathematics in Corwin's paper, phi and theta can be varied independently. The phi+theta=90 condition seems to be only a limitation of the "sabcor" program that only asks for phi in its input file. Peter -- -------------------------------------------------------------- Peter Pfalzer Universitaet Augsburg Tel: +49-821-598-3215 Lehrstuhl fuer Experimentalphysik II Fax: +49-821-598-3411 Universitaetsstr. 1 D-86135 Augsburg Germany Peter.Pfalzer@physik.uni-augsburg.de --------------------------------------------------------------